Cooling system utilizing a reciprocating piston

ABSTRACT

Cooling in the supersonic region of a compressible fluid is disclosed. The fluid is accelerated by a reciprocating piston to a velocity equal to or greater than the speed of sound in the fluid in an evaporator. No conventional mechanical pump is required to accelerate the fluid. A phase change of the fluid due to a pressure differential may be utilized to transfer heat from an element to be cooled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to cooling via a supersonicfluid flow cycle. More specifically, the present invention is related tocooling systems that establish a supersonic cooling cycle using areciprocating piston.

2. Description of the Related Art

Vapor compression systems are used in many cooling applications such asair conditioning and industrial refrigeration. A vapor compressionsystem generally includes a compressor, a condenser, an expansiondevice, and an evaporator. In a prior art vapor compression system, agas in a saturated vapor state is compressed to raise the temperature ofthat gas, the gas then being in a superheated vapor state. Thecompressed gas is then run through a condenser and turned into a liquid,and heat is rejected from the system. The condensed and liquefied gas isthen taken through an expansion device, which drops the pressure and thecorresponding temperature. The resulting refrigerant is then boiled inan evaporator, with the refrigerant absorbing heat. The saturated vaporis then returned to the compressor.

FIG. 1 illustrates a vapor compression system 100 as might be found inthe prior art. In the prior art vapor compression system 100 of FIG. 1,compressor 110 compresses the gas to (approximately) 238 pounds persquare inch (PSI) and a temperature of 190° F. Condenser 120 thenliquefies the heated and compressed gas to (approximately) 220 PSI and117° F. The gas that was liquefied by the condenser 120 is then passedthrough the expansion valve 130 of FIG. 1. By passing the liquefied gasthrough expansion valve 130, the pressure is dropped to (approximately)20 PSI.

A corresponding drop in temperature accompanies the drop in pressure,which is reflected as a temperature drop to (approximately) 34° F. inFIG. 1. The refrigerant that results from dropping the pressure andtemperature at the expansion value 130 is boiled at evaporator 140.Through boiling of the refrigerant by evaporator 140, a low temperaturevapor results. The vapor is illustrated in FIG. 1 as having atemperature of (approximately) 39° F. and a corresponding pressure of 20PSI.

The cycle carried out by the system 100 of FIG. 1 is an example of avapor compression cycle. Such a cycle generally results in a coefficientof performance (COP) between 2.4 and 3.5. The COP, as illustrated inFIG. 1, is the evaporator cooling power or capacity divided bycompressor power. It should be noted that the temperature and PSIreferences that are shown in FIG. 1 are exemplary and are for thepurpose of illustration only.

FIG. 2 illustrates the performance that might be expected of a vaporcompression system similar to that illustrated in FIG. 1. The COPillustrated in FIG. 2 corresponds to a typical home or automotive vaporcompression system operating at an ambient temperature of(approximately) 90° F. The COP shown in FIG. 2 corresponds to a vaporcompression system utilizing a fixed orifice tube system.

A system like that illustrated in FIG. 1 and FIG. 2 typically operatesat an efficiency rate or COP that is far below that of system potential.To compress gas in a conventional vapor compression system like thatillustrated in FIG. 1 (system 100) typically takes 1.75-2.50 kilowattsfor every 5 kilowatts of cooling power. This exchange rate is less thanoptimal and directly correlates to the rise in pressure times thevolumetric flow rate. Degraded performance is similarly and ultimatelyrelated to performance (or lack thereof) by the compressor 110.

Haloalkane refrigerants such as tetrafluoroethane (CH₂FCF₃) are inertgases that are commonly used as refrigerants in refrigerators andautomobile air conditioners. Tetrafluoroethane has also been used tocool over-clocked computers. These gases are referred to as R-134 gases.The volume of an R-134 gas can be 600-1000 times greater than itscorresponding liquid form. This multiplier shows that the theoreticalefficiency of a system utilizing an R-134 gas is much higher than iscurrently being realized, and evidences the need for an improved coolingsystem that more fully recognizes system potential and overcomestechnical barriers related to compressor performance.

In light of the theoretical efficiencies of systems using haloalkanes orother fluids, there is a need in the art for an improved cooling systemthat more fully recognizes system potential and overcomes technicalbarriers related to compressor performance. There is a further need fora cooling system that operates without the use of a conventionalmechanical pump.

SUMMARY OF THE CLAIMED INVENTION

A first claimed embodiment is for a cooling system. The system includesa fluid flow path with a converging/diverging nozzle positioned therein.A reciprocating piston is positioned in the converging/diverging nozzle,and a driving mechanism is coupled to the reciprocating piston to impartlinear motion to the reciprocating piston. The motion of thereciprocating piston accelerates a fluid in the fluid flow path so thatthe fluid flows in the critical flow regime. The fluid undergoes apressure change so that the temperature of the fluid is reduced, therebyallowing heat to be exchanged with an element to be cooled.

A supersonic cooling method is also claimed. The method includes drivinga reciprocating piston positioned within a converging/diverging nozzleto impart linear motion to the piston. The motion of the pistonaccelerates the fluid to a velocity equal to or greater than the speedof sound in the fluid. The acceleration also creates a low pressureregion in which the fluid undergoes a phase change and a decrease intemperature. Heat may be exchanged either directly though the walls ofthe converging/diverging nozzle or via a heat exchange mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a vapor compression cooling system asmay be found in the prior art.

FIG. 2 is a pressure-enthalpy graph for a vapor compression coolingsystem like that illustrated in FIG. 1.

FIG. 3 is a sectional view of an exemplary supersonic cooling unitutilizing a reciprocating piston.

FIG. 4 is a pressure-enthalpy graph for a supersonic cooling system asdescribed herein.

FIG. 5 illustrates a method of supersonic cooling utilizing areciprocating piston.

DETAILED DESCRIPTION

Embodiments of the present invention implement a supersonic coolingcycle that increases efficiency as compared to prior art coolingsystems. A system utilizing the present invention may operate at a COPof 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater,7 or greater, 8 or greater, 9 or greater, 10 or greater, 20 or greater,or 50 or greater. Embodiments of the present invention do not require acompressor or a conventional mechanical pump to operate. In place ofthese components is an electric motor or other driving mechanism thatimparts a driving force. The elimination of the need for a conventionalmechanical pump is beneficial in that the supersonic cooling systemincludes cavitation as part of the cooling cycle. Since cavitation istypically detrimental to the operation of a conventional mechanicalpump, the elimination of the conventional mechanical pump benefits theoperation of the system.

Part of the increase in COP for systems utilizing the supersonic coolingcycle with a reciprocating piston is due to the fact that such systemsdo not need to compress a gas as otherwise occurs at compressor 110 in aprior art vapor compression system 100 like the one shown in FIG. 1. Asupersonic cooling system 300, as illustrated in FIG. 3, operates byaccelerating a working liquid, which may be water, through a novel witha converging and diverging configuration (a converging/diverging nozzle)305.

A ‘converging/diverging’ configuration is generally representative of anozzle design that includes an inlet, throat, and exit with a continuousflow path in fluid communication with each section. The inlet sectionreceives a fluid, which is ultimately expeller at the exit portion. Thediameter of the flow path decreases (i.e., converges) from the inletportion to the throat portion of the nozzle. The nozzle then expands(i.e., diverges) from the throat to the exit portion of the nozzle. Theconverging/diverging nozzle 305 may be advantageously positioned in thevertical orientation shown in FIG. 3.

Because the supersonic cooling system 300 utilizes theconverging/diverging nozzle 305 to generate a cooling effect as furtherdescribed herein, the system 300 does not require the use of a condenser120 as does the prior art compression system 100 of FIG. 1. The system300 utilizes a working fluid that flows through a fluid flow path. Thefluid flow path includes the converging/diverging nozzle 305. Theworking fluid may be any suitable refrigerant chosen by a user of thesystem 300. The system 300 may utilize water as the working fluid toeliminate green house gas emission considerations.

The working fluid is accelerated in the converging/diverging nozzle 305by a reciprocating piston 310. The reciprocating piston 310 is coupledto a driving mechanism that imparts reciprocating linear motion to thepiston. The driving mechanism may be a crankshaft, a linear actuator, ora cam system. The driving mechanism may be powered by any suitabledriving device, such as an electric motor.

The velocity of the linear travel and the size of the reciprocatingpiston 310 are selected based on factors unique to a particularinstallation. The factors may include, but are not limited to, theworking fluid utilized in the installation and the amount of coolingpower desired. The construction of the reciprocating piston 310 may bedesigned to ensure that the reciprocating piston 310 imparts sufficientsuction on the working fluid to accelerate the fluid to at least thespeed of sound in the fluid.

Fluid flow into and out of the converging/diverging nozzle 305 may becontrolled by a pair of check valves. A first check valve 315 ispositioned upstream of an inlet 320 of the converging/diverging nozzle305. The first check valve 315 ensures that working fluid only entersthe inlet 320 of the converging/diverging nozzle 305 with limited or nobackflow. A second check valve 325 is positioned downstream of an outlet330 of the converging/diverging nozzle 305. The second check valve 325ensures that working fluid flows only outward through the outlet 330with backflow eliminated or greatly limited. The outlet 330 may beinstalled at a position just below the lowest point of travel of thereciprocating piston 310.

As an alternative, the reciprocating piston 310 may be configured toimpart a positive pressure on the working fluid to accelerate the fluidto a velocity greater than or equal to the speed of sound in the fluid.In such a case, the reciprocating piston may be disposed at the inlet320 or upstream from the inlet 320 of the converging/diverging nozzle305. In a first cycle the piston 310 may draw fluid into the inlet 320,and in a subsequent second cycle the piston 310 may drive the fluidthrough the converging/diverging nozzle 305. The positive pressure maybe provided by the decreasing volume between the piston and the inlet320 during the second cycle.

The working fluid may be introduced to the converging/diverging nozzle305 from an accumulator 335 coupled to the inlet 320 of theconverging/diverging nozzle 305. The accumulator 335 may be utilized toregulate the flow of the working fluid, and to reduce fluctuations inthe flow. A pressure set valve 340 may be coupled to the accumulator tocontrol the pressure of the working fluid in the accumulator 335,thereby controlling the pressure of the fluid entering the fluid flowpath. The pressure in the accumulator 335 may be set to a pressure justabove the vapor pressure of the working fluid.

The working fluid may contain certain non-condensable components such asair. To remove the non-condensable components, a trap 335 may be coupledto the fluid flow path. The trap 335 may be equipped with a bleed valve355 to expel the non-condensable components from the fluid flow path.The trap 335 may be positioned at the highest point of the fluid flowpath to increase its efficiency. The cooling system 300 may need to beperiodically drained and/or recharged with working fluid. To this end, acharge/drain valve 345 is coupled to the fluid flow path.

The cooling cycle created by the system 300 is initiated with thereciprocating piston 310 at its lowest position in a cylindrical portionof the converging/diverging nozzle 305. The cooling cycle begins with anupward movement of the reciprocating piston 310 imparted by the drivingmechanism. As the reciprocating piston 310 moves upward, working fluidmay be drawn from the accumulator 335 through the first check valve 315.The working fluid is accelerated as it flows through theconverging/diverging nozzle 305 and reaches its maximum velocity in thethroat of the nozzle 305. At this point, the velocity of the workingfluid will be equal to or greater than the speed of sound in the workingfluid.

As the fluid is accelerated through the converging/diverging nozzle 305,the static pressure of the fluid at the throat drops below the vaporpressure of the fluid. Cavitation occurs so that the working fluid in atleast a part of the converging/diverging nozzle 305 is a dual phasefluid including the liquid phase and the vapor phase. The vapor phasemixing with the liquid working fluid reduces the speed of sound in theworking fluid. As the working fluid continues to flow through theconverging/diverging nozzle 305, still more vapor is formed throughevaporation (boiling) of the fluid caused by supersonic flow in theexpanding area of the converging/diverging nozzle 305. These factors mayallow the formation of a compression wave that is utilized in theacceleration of the working fluid.

Because the working fluid flows in at least a portion of theconverging/diverging nozzle 305 at a velocity equal to or greater thanthe speed of sound in the fluid, the cooling system 300 operates in thecritical flow regime of the working fluid. In this regime, the pressureof the fluid in the system 300 may remain almost constant and then‘jump’ or ‘shock up’ to the ambient pressure as the cooling cycle iscompleted.

Because cooling system 300 accelerates the working fluid and creates apressure differential through the linear movement of the reciprocatingpiston 310, cooling system 300 does not require the use of aconventional mechanical pump. The reduced amount of hardware required tooperate the cooling system 300—there is no need for either a compressoror a conventional mechanical pump—gives rise to a greatly improvedcoefficient of performance (COP) for the system.

When the reciprocating piston 310 reaches the top of its stroke in thecylindrical portion of the converging/diverging nozzle 305, the movementof the piston stops, and acceleration of the fluid is also stopped. Thevapor bubbles in the fluid continue to rise in the converging/divergingnozzle 305 until the bubbles reach the lower surface of thereciprocating piston 310. The static pressure in theconverging/diverging nozzle 305 increases until the bubbles collapse andthe fluid flows out of the converging/diverging nozzle 305 through theoutlet 330.

During the acceleration phase of the cooling cycle, the phase change andpressure differential in the converging/diverging nozzle 305 generatethe cooling effect for the supersonic cooling system 300. The workingfluid absorbs heat from the walls of the converging/diverging nozzle305. Heat transfer to an object to be cooled may be facilitated by aheat exchanging mechanism 350. The heat exchanging mechanism 350 mayinclude fins on the surface of the converging/diverging nozzle 305. Acirculating fluid heated by the object to be cooled may be thermallycoupled to the heat exchanging mechanism 350. FIG. 4 illustrates apressure-enthalpy graph for a supersonic cooling system operating inaccordance with FIG. 3.

In the supersonic cooling system 300, the working fluid travels throughthe fluid flow path to generate a cooling effect via the methoddelineated in FIG. 5. In a step 510, the motive force for moving thefluid is provided by linear motion of the reciprocating piston 310. In astep 520, the working fluid is drawn through inlet 320 into theconverging/diverging nozzle 305 at least in part by suction created bythe linear motion of the reciprocating piston 310.

In a further step 530, the fluid is accelerated through theconverging/diverging nozzle 305. During the acceleration step 530, acavitation effect is created in the converging/diverging nozzle 305. Asthe working fluid flows through the converging/diverging nozzle 305, thesuction generated by the linear motion of the reciprocating piston 310accelerates the working fluid. A decrease in pressure and a phase changein the working fluid result in a lowered temperature of the fluid tocreate a cooling effect in step 540.

Critical flow rate, which is the maximum flow rate that can be attainedby a compressible fluid as that fluid passes from a high pressure regionto a low pressure region (i.e., the critical flow regime), allows for acompression wave to be established and utilized in the critical flowregime established in the converging/diverging nozzle 305. Critical flowoccurs when the velocity of the fluid is greater than or equal to thespeed of sound in the fluid. In critical flow, the pressure in theconverging/diverging nozzle 305 will not be influenced by the exitpressure. In step 550, the working fluid may ‘shock up’ to the ambientconditions as the fluid exits the converging/diverging nozzle 305.

The pressure change of the fluid in the system 300 may include a rangeof approximately 20 PSI in the low pressure region to 100 PSI in thehigh pressure region. In some instances, the pressure may be increasedto more than 100 PSI or more than 150 PSI. In some embodiments, the lowpressure region may be at a pressure of less than 1 PSI. Forinstallations using water as the working fluid, an initial pressure ofthe fluid may be 30 PSI. Depending on the characteristics of any givenapplication, the pressure change range may vary from that describedimmediately above.

The cooling effect of the system 300 may be realized in an object to becooled by putting the object in direct contact with theconverging/diverging nozzle 305. The transfer of heat from the object tobe cooled into the system 300 may also be accomplished in an optionalstep 560. In optional step 560, the working fluid is thermally coupledto a heat exchange mechanism 350. The heat exchange mechanism 350 may bethermally coupled to a heated circulating fluid from the object to becooled by the supersonic cooling system 300.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. The descriptions are not intended to limit the scope of theinvention to the particular forms set forth herein. Thus, the breadthand scope of a preferred embodiment should not be limited by any of theabove-described exemplary embodiments. It should be understood that theabove description is illustrative and not restrictive. To the contrary,the present descriptions are intended to cover such alternatives,modifications, and equivalents as may be included within the spirit andscope of the invention as defined by the appended claims and otherwiseappreciated by one of ordinary skill in the art. The scope of theinvention should, therefore, be determined not with reference to theabove description, but instead should be determined with reference tothe appended claims along with their full scope of equivalents.

1. A cooling system, the system comprising: a fluid flow path includinga converging and diverging nozzle; and a reciprocating piston positionedwithin the converging and diverging nozzle, wherein linear motionassociated with the reciprocating piston accelerates a fluid in thefluid flow path such that the fluid flows in the critical flow regimeand undergoes a pressure change while traversing the flow path at theconverging and diverging nozzle, the pressure change reducing thetemperature of the fluid.
 2. The system of claim 1, further comprising adriving mechanism coupled to the reciprocating piston to impart linearmotion to the reciprocating piston.
 3. The system of claim 1, whereinthe acceleration of the fluid flow by the reciprocating piston generatesa compression wave that influences the temperature of the fluid.
 4. Thesystem of claim 1, wherein the linear motion of the reciprocating pistongenerates suction, the suction inducing cavitation in the fluid.
 5. Thesystem of claim 1, wherein the converging and diverging nozzle isthermally coupled to an element to be cooled by the fluid.
 6. The systemof claim 1, wherein the converging and diverging nozzle is thermallycoupled to a heat exchange mechanism.
 7. The system of claim 1, whereinthe fluid pressure change induced by the reciprocating piston is fromapproximately 150 PSI to approximately 10 PSI.
 8. A cooling method, themethod comprising: driving a reciprocating piston within a convergingand diverging nozzle to impart linear motion, wherein the linear motionof the piston accelerates fluid flowing through the converging anddiverging nozzle to a velocity equal to or greater than the speed ofsound in the fluid; and exchanging heat introduced into the fluid flowpath via a cooling effect created during a phase change of the fluid,the phase change induced through the acceleration of the fluid throughthe converging and diverging nozzle by the reciprocating piston.
 9. Themethod of claim 8, wherein a compression wave is created in the fluid asthe fluid passes from a high pressure region to a low pressure region ofthe converging and diverging nozzle.
 10. The method of claim 9, furthercomprising creating cavitation, the cavitation created as a result ofthe linear motion of the reciprocating piston, and wherein thecavitation assists in formation of the compression wave.
 11. The methodof claim 8, wherein the exchange of heat occurs at a heat exchangingmechanism thermally coupled to the converging/diverging nozzle.
 12. Themethod of claim 8, wherein the linear motion of the reciprocating pistoncreates suction that draws the fluid through the converging/divergingnozzle.
 13. The method of claim 8, further comprising moving the fluidfrom a high pressure region to the low pressure region as the result ofa suction effect generated by the reciprocating piston.
 14. The methodof claim 8, wherein the phase change corresponds to a pressure change ofthe fluid.
 15. The method of claim 14, wherein the pressure change ofthe fluid occurs within a range of approximately 0.5 PSI toapproximately 175 PSI.
 16. The method of claim 14, wherein the pressurechange of the fluid involves a change to a pressure greater than orequal to 200 PSI.
 17. The method of claim 14, wherein the pressurechange of the fluid involves a change to a pressure less than or equalto 10 PSI.
 18. The method of claim 9, wherein the fluid shocks up to anelevated pressure as the fluid exits the low pressure region.
 19. Acooling system, the system comprising: a fluid flow path including aconverging and diverging nozzle; and a reciprocating piston in fluidcommunication with the converging and diverging nozzle, thereciprocating piston accelerating a fluid in the fluid flow path to avelocity greater than or equal to the speed of sound in the fluid byimparting motion to the fluid such that the fluid flows in the criticalflow regime and undergoes a pressure change while traversing the flowpath at the converging and diverging nozzle, the pressure changereducing the temperature of the fluid.
 20. The cooling system of claim19, wherein the reciprocating piston is upstream from a fluid inlet ofthe converging and diverging nozzle.